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Make a parabolic solar dish from an 8 by 4 sheet of plastic (without too much waste)

I need to make a half parabolic dish for a solar cooking project and I am trying the "cone method" .  Basically my dish will be made from concentric cones to mimic a parabolic dish and  to give the desired concentration of light.  For me a 6 inch ball of fire at the focus should work.
I am cheap and lazy  so I want to get maximum use from an 8 by 4 sheet of plastic without having to cut it into a thousand petals and still have it work with the rest of the design.
 What I came up with will probably work for me.
But I wanted to share the method so that it can work for you, and perhaps for disaster relief too.
Brian
 
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Step 1: Design of the parabolic curve

Picture of Design of the parabolic curve
I did this with an improvised t-square and basic technical drawing tools,wrinkled paper.  and a calculator. So there are probably Measurement errors a plenty.
However the method is valid.
I will leave the image notes to explain things for the moment.
I start with the mirror straight across from the target ball because  if you start anywhere else, it is hard to figure out how big your dish will be.
There are 2 ways to do the mirror angle. 
The mirror is set up at half the angle of the light hitting the mirror and the light bouncing away from the mirror.   The parallel lines method is much quicker than measuring angles but you need to check as errors creep in.
I never learned cad.
I am sure this will be perfected on computer aided design programs.

Step 2:

Picture of
IMG_2252.JPG
I cut out my concentric cones on a sheet of corrugated plastic and then had to glue the mylar on. I used wheat paste .  I simply laid the sheet of mylar over the sheet of corrugated plastic and it stuck. Later, I used a knife to simply cut the mylar to the same patern as the sheet of corrugated plastic. It was easy!
rimar20003 years ago
Your design will prove to be good only if you can cook normally during a cold and windy day. I get the impression that this configuration will not succeed. Too many wrinkles. And 112º C is too low, specially in summer.
gaiatechnician (author)  rimar20003 years ago
It was about 6 pm and cloudy with the sun low in the sky. Pretty meaningless. I know about the wrinkles and that can be fixed. It is conic sections so wrinkles will be less than in the petal type dishes. It curves in just one direction. I used wheat paste as the glue and it did not set up. So yes indeed, I made lots of mistakes.
I will make more mistakes by the time I am finished.
rimar20003 years ago
Brian, your result is good, but it would be better if instead of thin film you use thicker, about 0.03 cm of metalized acetate or polypropilene. It makes much (but much!) less wrinkles.
gaiatechnician (author)  rimar20003 years ago
Hi, Rimar, Thanks for the comment, I will change the reflector film when this one fails completely. I might fully redo the dish too, right from the drawing stage. If I start again from scratch, I can do the holes for the rotating with grommets, and I can mark and punch holes for the bamboo at the same time. And I can make the metal frame the right size before I join the dish together. The only reflective material that are readily available to me is this thin mylar and kitchen foil.
I will look into finding the other versions.
I also made a mistake using wheat paste as the glue. It couldn't dry between the layer of plastic and the layer of mylar. The problem for me right now is work pressure. I am fully booked for the next 2 months. (Overbooked, so I must work weekends too). I will put up some more videos when I get a chance and maybe other people will try it.
Thank you
Brian
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